Surgery through a trocar inserted cannula and particularly with an opening through the tissue of an animal or human abdominal wall has become an important means to minimize the extent of surgical invasion. The lessening of invasion improves the cosmetic result, shortens recovery and lowers the cost. Endoscopic internal surgical procedures and equipment are available and in use for a variety of medical operations including gall bladder, bowel and gynecological surgery. A proper and simple instrument to open the passage through the abdominal wall and avoid injury to internal organs during the placement of the cannula by means of a trocar is needed.
U.S. Pat. No. 3,595,239 discloses a catheter tube having an obturator in the form of an electrode passing coaxially therethrough. The obturator electrode is connected to an electrosurgical generator in order to provide high frequency energy used to divide or cut tissue thereby forming a passage for the catheter to pass through. The tip of the obturator extends beyond the catheter tip and is capable of cutting. The catheter is moved along with the obturator electrode by means of a ring disposed about the obturator proximal to the tip and inside the tip of the catheter. There is no disclosure of any means for sensing the impedance or load associated with the energy required to do the cutting during insertion of the obturator tip.
U.S. Pat. No. 4,856,530 discloses an automatic system for determination of the size of a catheter distal tip remotely at the proximal end of the catheter. A capacitor at the distal tip is connected to a pair of wires which extends proximally to a microprocessor which determines the decay constant of the capacitor and thereby establishes the catheter size. There is no disclosure of interactive measurement of the energy required for cutting tissue by impedance load or otherwise.
U.S. Pat. No. 4,651,280 discloses a microprocessor with a preset control for an electrosurgical unit during a transurethral resection. A current monitoring probe about the output of the electrosurgical unit is responsive to load such that differences in the tissue and in inclusions therein are measured as changes in conductivity which are directly related to the load during the resection. Variation and output power of the electrosurgical unit are a measure of what tissue is resected. The current changes are sensed by a peak detector, connected to a phase shifter so that a control signal relative to the current level can be provided to a sample and hold circuit to accumulate data that can be converted by an analog to digital converter for processing by a microprocessor.
U.S. Pat. No. 3,601,126 teaches delivery of power at a constant level to the active electrode as it engages the tissue and during the entire operational procedure. A reference current amplitude is used to maintain the cutting current constant. There is no disclosure of monitoring the energy or preventing the increase of energy upon entry into an internal cavity of the body.
U.S. Pat. No. 4,126,137 has voltage and current sensors which are used to monitor power used during cutting. The circuit suggests that to make linear the power delivery at high and low impedance the power is increased and decreased, respectively. That is, with changes in impedance the power is increased with increasing impedance. There is no appreciation of the need to cut off power with increased impedance to provide safety.
U.S. Pat. No. 4,231,372 has a current sensor in series with the ground. A comparator sets a threshold at which an alarm or disabling circuit functions as the current exceeds the threshold. Reset of the operation is timed and automatic so there is no safety responsive to an impedance increase upon reaching an inner cavity of the body.
U.S. Pat. No. 4,232,676 has a knife blade which cuts and cauterizes the incision and in so doing self limits the current flow at the knife. Specifically, the blade has electrodes across which current flows when there is a conductive path after cutting the current cauterizes the incision sealing the wound and eliminating the current path. No recognition of the impedance change due to the inner cavity of the body is disclosed.
U.S. Pat. No. 4,281,373 has a circuit responsive to the needs of the cutting effort required. If the power is inadequate to prevent sticking of the cutter in the tissue the power is increased. There is no safety circuit responsive to the change in power required when the cutter has reached a body cavity.
U.S. Pat. No. 4,416,277 monitors the contact resistance of the return electrode maintaining the impedance within a range to prevent burns. Automatic setting of the upper limit as a function of load is taught so the power is regulated. There is an alert but no shut off when a body cavity is entered and high impedance is detected.
U.S. Pat. No. 4,494,541 senses capacitance between the body and an electrically conductive layer isolated from the body but part of the return electrode. If the capacitance is not within a certain range an alarm is produced. Although current to the active electrode may be stopped if an alarm condition is detected, it is not a function of having reached an internal cavity of the body.
U.S. Pat. No. 4,498,475 has an intensity controlled by changing resistance which controls a transistor that turns the power on and off. There is no detection of impedance change at the inner body cavity.
U.S. Pat. Nos. 4,601,710 and 4,654,030 teach trocar tubes with a shielding sleeve in addition to the tube. The shielding sleeve may project beyond the end of the trocar thereby shielding the tip of the trocar while in the body cavity.
U.S. Pat. No. 4,535,773 discloses techniques for shielding the sharp tip of a trocar by either interposing an extensible shielding sleeve or retracting the trocar into its tube. With regard to the latter, a solenoid operated detent holds the trocar in an extended position relative its tube and electronic sensing in the tip of the trocar is used to activate the detent for release. Nothing in this reference has any disclosure of an impedance responsible circuit used to regulate an electrosurgical generator, attached to an electrosurgical cutting tip. Sensors and switches are used in conjunction with the probe which retracts during penetration. In particular, the probe extends beyond the cutting surface once the abdominal wall has been traversed. The sensors can be connected to an oral or visual signal to indicate completion of the puncture. The switches could be mechanical or magnetic, be tripped by a sleeve in the puncturing instrument, a probe or a spring wire protruding from the tip or blade of a sharp pointed cutter. Multiple sensors in the cutting blade and the cannula can be used to signal circuit of the penetration position. No disclosure of an impedance sensitive circuit is in this rather extensive disclosure.
U.S. Pat. No. 4,919,653 discloses a device for locating epidural space. The release of force on the tip of a needle triggers an alarm which activate a solenoid latch permitting the needle and its sleeve to move in a cannula in response to an activated electromagnet such that the distal end moves 2 mm into the epidural space. Pressure sensors detect when the depression or release of pressure occurs as the needle enters the epidural space. The pressure signal is converted to produce the voltage difference between the sensor and the potentiometer. This difference is shown on a meter. The pressure sensor can be a small membrane with electrical contacts which are closed in the unloaded position and open when the membrane moves when the epidural space is reached. The passage of current through the contacts keeps the circuit open by means of a relay.
To safely place a cannula by a trocar technique requires knowledge of the position of the distal cutting tip of the stylet used to open the passage for the cannula through the animal or human tissue of the abdominal wall. A device to instant indicate when the cutting tip has passed through the tissue and reached the inside of the body is needed so that the internal organs are not injured. Because the organs fill the inside cavity and are close to the wall there is the possibility of injury before the surgeon can stop advancing the distal cutting tip.